Speedometer not work properly

[Kristopher Sciler]

I have a 1998 silverado z71 replaced trans and transfer case now speedometer shows im going 10mph faster than actual even replaced speed sensor in tailshaft. Any idea what the problem could be.

 

Edited November 10, 2020 by Kristopher Sciler

[Brian Lindsey]

i also have a 98 and my speedo is off by 5mph, do you have the same size tires that are listed  on the door label, that will affect your speedometer, the only other suspect i can think of is your speed sensor

[thx1138v2]

The only thing I can think of is that the reluctor ring on the new transmission has more cogs than the one in the old transmission.

[ChevroletTough]

That's what I'd think as well (the cog), did you replace (upgrade) your tire size at all?

[Jamal Iqbal]

On 11/10/2020 at 9:19 PM, Kristopher Sciler said:

I have a 1998 silverado z71 replaced trans and transfer case now speedometer shows im going 10mph faster than actual even replaced speed sensor in tailshaft. Any idea what the problem could be.

 

You have to change the speed sensor. 

I had the same problem and then the speed indicator failed. First I changed the speedometer without success and then the speed sensor on the gearbox.